This invention relates to a thermal imaging system incorporating a wedge shaped ferroelectric transducer of the variety disclosed and claimed in U.S. Pat. No. 3,866,189 as the image sensing element. In particular, this invention utilizes a heretofore unrecognized thermal sensitivity characteristic of the wedge shaped ferroelectric transducer by modification of the surface of the transducer facing the thermal source such that discrete portions of that surface are individually responsive to the thermal source. Thus this invention may be considered an improvement over the invention disclosed and claimed in U.S. Pat No. 3,866,189. As in the preceding invention, it is the saturation level state of the square hysteresis loop material which affords useful information and, as in the preceding invention, a ramp voltage readout technique is employed to obtain the saturation level state information. In this instance, thermal energy exposure of the ferroelectric transducer alters the saturation level state. There are numerous applications where it is desirable to detect an image thermally where large volume or short lived transducers are unusable. Additionally, there are applications where it may be required to detect an object's general shape and motion along one or two axes, such as for use on an assembly line, but without the attendant complexity and cost of a complete vidicon system.
Therefore, a need has been created for a small, long lived thermal imaging transducer and system which is not complex. This invention is of a ferroelectric thermal imaging transducer and system which can detect either a moving or stationary object and generate a time varying voltage indicative of the general shape and motion along one or both axes. At least 250 bits of thermal information can be readout from this transducer if the ferroelectric is 10.5 millimeters in length, and configured as a single axis device.
If the ferroelectric is built in a two axes configuration, 2 centimeters by 1 centimeter, at least 1000 bits of thermal information can be readout in a 50 by 20 bit grid.
Although ferroelectric devices have been used in the past to operate as image transducers, they have required either a collimated polarized light beam and photoconductive coating, or else had to be used as a target in an evacuated cathode ray tube. Both these methods are relatively bulky, or have relatively short lives. Pyrolectric vidicons, to be workable, must be panned or else have a shutter interrupt the thermal energy source. The present invention does not require any such artifact.
What I have discovered is that there is a method to read thermal imaging information out of a ferroelectric chip, yet use only two electrical connections or, at most, three, and do this is a very small volume.
The readout can be effected without recourse to cathode ray tubes, collimated polarized light or panning or image interruption. Accordingly, it does not need mechanical devices for panning or interrupting.
Further, I have devised an electronic technique which, when used in conjunction with the transducer, can selectively readout those portions of the field of view desired.